The objective of this supplement is to expand the Core Epidemiological Study of Obstructive Lung Diseases by obtaining serum IgE levels on blood samples already obtained from the 3000 of the 3350 eligible subjects enrolled in the study. The objective is to determine the relationship of serum IgE levels to the development and natural history of various types of obstructive lung diseases. Furthermore, this work will: 1) clarify the relationships of IgE to allergy skin test reactivity, 2) clarify the characteristics of IgE levels in a normal population, and 3) test the hypothesis that serum IgE levels are a reflection of genetic atopic status. IgE determinations on the 3000 sera will be performed using a radioimmunoassay (radio-immunosorbant test). These results will be related to questionnaire and objective test data already obtained from these subjects. This data includes extensive respiratory history information, flow-volume curves, family history and tree information, allergy skin test reactivity, closing volumes, reactions to coccidioidin and histoplasmin skin tests, peripheral blood eosinophils and serum precipitans.